| Question | Answer | Note |
| Check IP | ip addr show eth0 | grep inet | awk ‘{ print $2; }’ | sed ‘s/\/.*$//’ |
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| List block devices, check mount point | lsblk |
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| Disable password login | /etc/ssh/sshd_config -> PubkeyAuthentication no service sshd restart |
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| Back up as root | su root gksu deja-dup-preferences gksu “deja-dup – -backup” |
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| Extend LVM partition size | 1. use GParted to extend LVM partition’s volume size (VG size) 2. use “vgdisplay” to find free PE size of LVM root partition 3. use “lvextend -l +PE_size /dev/name_vg/root“ to extend root’s logical volume size 4. “resize2fs /dev/name_vg/root” | pvs, vgs, lvs, pvdisplay, vgdisplay, lvdisplay, pvscan |
| Add cron job | sudo su – crontab -e schedule | e.g. schedule: 0 2 * * * /opt/gitlab/bin/gitlab-rake gitlab:backup:create CRON=1 |
| Add sticky bit to disable/enable delete permission by others | chmod +t /directory chmod -t /directory |
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| Remove a user from a group | sudo deluser username group_name |
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| Add a user to a group | usermod -aG group_name username |
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| Add a group | groupad -g Group_ID Group_Name check all the groups: cat /etc/group |
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| To check special group | grep ‘^sudo’ /etc/group |
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| Add feature to support switch between ubuntu-desktop and gnome | sudo apt-get install gnome-session-fallback |
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| change ownership of all files of directory: (-R is for all files) | sudo chown -R $USER:$USER __directory__ |
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| Grant sudo to user | user mod -aG sudo username |
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| To enable a root user | sudo passwd root |
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| To disable the root account, type | sudo passwd -dl root |
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| Check memory and cpu status | top free -m |
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| Hash miss match | apt-get clean rm -rf /var/cache/apt/* rm -rf /var/lib/apt/lists/* apt-get update |
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| Check ports status | sudo netstat -lnp |
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| Update network config | sudo ip addr flush enp0s25 sudo systemctl restart networking.service | Edit /etc/network/interfaces |
| Run shell script in background | e.g. nohup sudo xxxx.sh |
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| Run at bootup time | put a script in the /etc/init.d/ directory | e.g. /etc/init.d/go.py |
| When using the command shell, prefixing a command with nohup prevents the command from being aborted automatically when you log out or exit the shell. | nohup –help | –version | nohup command [command-argument …] |
| Add an additional hard drive | use gparted to create a new partition sudo mkdir /newPartition sudo nano /etc/fstab to add: /dev/sda6 /newPartition ext4 defaults 0 0 sudo mount /newPartition |
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| Install samba | apt install samba apt install system-config-samba touch /etc/libuser.conf system-config-samba adduser username smbpasswd -a username service smbd restart |
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